(a) Field of the Invention
The invention relates to a method for preventing and/or inhibiting HLA alloimmune response to platelet transfusion, by presensitizing platelets with at least one monoclonal HLA antibody.
(b) Description of Prior Art
Many patients who receive platelet transfusions become alloimmunized, rendering them refractory to subsequent platelet transfusions. It is thought that xe2x80x9ccontaminatingxe2x80x9d HLA Class II bearing antigen presenting cells (APC) augment the production of these alloantibodies and various methods have been used to inactivate or remove these xe2x80x9ccontaminatingxe2x80x9d cells, including the use of ultraviolet radiation and leucofiltration. Although these methods have been successful at reducing the incidence of primary alloimmunization, many multi-transfused patients still become alloimmunized. For those patients already alloimmunized by prior transfusion or pregnancy, even leucodepleted platelets can stimulate a secondary alloimmune response. Animal studies suggest that extreme leucodepletion may be detrimental to inhibiting immune responses to transfusions, suggesting that the ability of leucodepletion to decrease alloimmunization may have reached its threshold.
Antigen-specific IgG, when injected at the time of antigen exposure, can induce a strong suppression of the immune response. The immunosuppressive effect is particularly effective with large antigen systems, such as red blood cells, and this is currently applied to the prevention of fetal erythroblastosis in Rh negative women by administration of anti-D IgG. Pretreatment of whole blood with polyclonal alloantisera has been shown to prevent alloantibody production in rat models of transfusion. More refined studies in rats have shown that pretreatment of platelets or leukocytes with alloantisera also inhibits the alloimmune response to platelet transfusion.
Antibody/antigen complexes can inhibit immune responses and it has been hypothesized in the immunological literature that this down-regulation of humoral responses is likely contributed to by a negative feedback pathway mediated by B cell Fcy receptor (FcyR) co-crosslinking with the B cell Ig receptor (BCR), resulting in the B cell entering a xe2x80x9cnon-responsivexe2x80x9d state mediated by activation of a negative feedback pathway at the level of BCR signaling.
An alternate theory developed is that alloimmune serum from alloimmunized individuals contains elevated levels of an anti-IgG (i.e. an IgG rheumatoid factor (RF)) and this IgG RF contributes to or mediates a decrease in the alloimmune response. Purified IgG RF from the serum of alloimmunized rats exerts immunosuppressive effects in vivo and in vitro.
The inventors have shown previously that SCID mice, engrafted with human (Hu) peripheral blood lymphocytes (PBL) from alloimmunized donors are a valuable tool for studying alloimmunization and that transfusion of these Hu-PBL-SCID mice with human alloimmune sera presensitized platelets results in a decreased alloantibody response to further untreated platelet transfusions (Crow A R, et al., Br J Haematol 104:919, 1999).
In the present invention, a single dose of platelets presensitized with monoclonal HLA Class I antibody (either depleting or non-depleting) abrogated the alloantibody response to five subsequent untreated platelet challenges. FCR mediated B cell down regulation was not required for the alloimmune inhibition observed, since F(abxe2x80x2)2 fragments of monoclonal anti-HLA-A,B,C antibody completely abrogated the immune response whereas platelets treated with platelet-specific antibody or control murine IgG had no inhibitory effect.
It would be highly desirable to be provided with a new approach for inhibiting the human alloimmune response to platelet transfusion.
One aim of the present invention is to provide a new approach for inhibiting the human alloimmune response to platelet transfusion.
In accordance with the present invention there is provided a new method for inhibiting the human alloimmune response to platelet transfusion.
Since monoclonal antibodies can be made by recombinant means and the fine specificity of the antibody is not critical to inhibit alloimmunization, the present invention provides a new and practical approach for inhibiting the human alloimmune response to platelet transfusion.
In accordance with the present invention there is provided a method for preventing HLA alloimmune response to platelet transfusion, comprising the step of presensitizing platelets with at least one monoclonal antibody against HLA, a portion thereof, or xcex22-microglobulin, wherein the platelets if administered to a patient prevent an HLA alloimmune response from the patient.
The monoclonal antibody can be for example W6/32, L368, and MA2.1 ATCC accession numbers HB-95, HB-149, and HB-54, respectively wherein such antibodies are readily available without restrictions from the American Type Culture Collection (ATCC).
In accordance with the present invention there is also provided a method for inhibiting an HLA alloimmune response to platelet transfusion. The method comprises the steps of:
a) presensitizing platelets with at least one monoclonal antibody against HLA or a portion thereof; and
b) transfusing with the presensitized platelets of step a) to a patient, the presensitized platelets inhibiting an HLA alloimmune response from the patient. The HLA alloimmune response can still be prevented after at least two transfusions from the patient.
The term xe2x80x9cplateletsxe2x80x9d in the instant application is intended to also include, without limitation, platelet concentrates, platelet substitutes, platelet rich plasma, platelet poor plasma, lyophilized platelets, platelets fragments, red blood cells, red blood cell concentrates, leukocytes and buffy coats.
The monoclonal antibodies useful in the method of the present invention include, without limitation, monoclonal antibodies against either Public or Private epitopes of HLA. The monoclonal antibodies do not have necessarily to be against HLA as monoclonal antibodies against the xcex22-microglobulin (xcex22M) portion of HLA are also effective at alloimmune inhibition.
The expression xe2x80x9cmonoclonal antibodiesxe2x80x9d also meant to include without limitation murine monoclonal antibodies, recombinant MAbs, humanized MAbs, single chain MAbs, bispecific MAbs where one epitope is HLA orxcex22M, F(ab)xe2x80x22 and F(ab) fragments of these monoclonal antibodies.
The present invention can be used to protect or prevent alloimmunization. However, the method of the present invention can also be used for preventing refractoriness to subsequent transfusions in alloimmunized patients.
In accordance with the present invention, there is provided a method for preventing refractoriness to subsequent transfusions in an alloimmunized patient, comprising a) presensitizing platelets with at least one monoclonal antibody against HLA or a portion thereof, and b) transfusing the alloimmunized patient with the presensitized platelets of step a), the presensitized platelets preventing refractoriness to the transfusion.
In accordance with the present invention, there is provided a method for preventing an alloimmune disease or an alloresponse. The method comprises the steps of a) presensitizing platelets with at least one monoclonal antibody against HLA or a portion thereof; and b) transfusing with the presensitized platelets of step a) to a patient. The presensitized platelets inhibit an HLA alloimmune response from the patient.
The alloresponse may be for example an organ transplantation-related complication, such as an organ rejection.